Control valves (e.g., sliding stem valves, rotary valves, axial flow valves, globe valves, etc.) are commonly used in industrial processes, such as oil and gas pipeline distribution systems and chemical processing plants, to control the flow of process fluids. In some industrial processes, rotary valves such as, for example, butterfly valves are used to control the flow of process fluids. Butterfly valves are favored in certain applications because they are inexpensive to manufacture, relatively lightweight and provide quick and tight shut off.
Butterfly valves include a circular disk disposed within a valve body to regulate the flow of fluid through the valve. A shaft, which passes through a bore in the valve body, is coupled to the disk to rotate the disk within the valve body. A seal (e.g., a hard metal seal or a soft seal) is coupled or clamped to a surface of the valve body via a seal retainer. In a closed position, a sealing edge on the disk engages the seal to prevent the flow of fluid through the valve body.
Different types of seals are used for different applications. Typically, industrial process conditions, such as pressure, temperature, and the type of process fluids dictate the type of valve components needed, including the types of butterfly valve seals that may be used. It is generally known that relatively soft seals provide better sealing than harder seals because soft seals better conform to uneven sealing surfaces than relatively stiff (e.g., less compliant) seals. However, relatively soft seals generally have a lower operating temperature rating than hard seals because the softer materials tend to degrade or deteriorate (e.g., melt) in high temperature applications.
To be used in certain applications, the seals for butterfly valves may be required to pass specific tests and/or be certified under certain standards. For example, to be used in some applications, a seal for a butterfly valve may have to pass the American Petroleum Institute (API) 607 “Fire Test for Soft-Seated Quarter Turn Valves.” This standard covers the requirements for testing and evaluating the performance of straightway, soft-seated quarter-turn valves when the valves are exposed to fire conditions. Specifically, this test burns the valve at around 1800° Fahrenheit (F.) and then requires the valve to achieve shutoff once the valve cools. The API 607 test ensures that if an industrial plant or an area in an industrial plant catches fire, the valve can be properly shutoff to prevent the flow of process fluid through the piping distribution system. Therefore, this test requires a seal to provide a proper seal after being exposed to high temperatures. As mentioned above, relatively stiff or hard seals, such as metal seals, are often used in such an application because metal seals generally have rated operating temperatures that enable the seal to withstand high temperatures such as those involved in the above-noted testing. However, with such relatively stiff or hard seals, it may be difficult to achieve a desired tight shutoff of the valve, such as that achieved with a relatively soft seal.